The present invention relates to a high frequency current multiconductor cable and a feeding equipment for one or more movable bodies using the high frequency current multiconductor cable.
As for a known feeding equipment for feeding high frequency current from a power source by using a high frequency current multiconductor cable, there is one disclosed, e.g., in Japanese Patent Kokai Hei 6-153305.
In the feeding equipment, a line (induction line) to which a given high frequency current is fed from a power source device is laid along a guide rail (an example of movable line) for a carriage (an example of movable body), and the carriage is provided with a pickup coil which is fed from the induction line in a noncontact manner. In the carriage, connected in parallel with the pickup coil is a capacitor cooperating with the pickup coil to constitute a resonance circuit which resonates at the frequency of the induction line, the capacitor having a rectifying/smoothing circuit connected thereto. Further, connected to this rectifying/smoothing circuit is a stabilization power circuit for maintaining the output voltage at a reference value. Through an inverter, this stabilization power circuit feeds a motor, corresponding to a load, connected to the traveling wheels of the carriage.
The high frequency current fed from the power source device to the induction line concentrates near the conductor surface due to the skin effect, which means that the effective cross-sectional area of the conductor decreases, with the result that the resistance of the line becomes higher than when dc current is passed through the line; the resistance also increases with increasing frequency. In order to avoid the loss caused by the resistance increasing due to the skin effect, a litz wire (enamel-coated, small-diameter conductors stranded together) is widely used as a cable used as a line for passing high frequency current therethrough.
However, the known cable described above poses the following problems.
1. The cable using the litz wire makes it necessary to remove the enamel and solder when it is to be connected; thus, the terminal preparation is troublesome and it is difficult to maintain the quality and reliability of such terminal preparation.
2. Litz wires, which are expensive, form a factor in high installation cost.
To solve such problems in a simple manner, it may be contemplated to use a multiconductor cable formed by bundling a plurality of vinyl-coated conductors. Multiconductor cables require no soldering and allow the use of conventional crimp terminals, thus extremely facilitating the terminal preparation, and their cost is about half that of litz wires.
However, as a factor which causes an increase in the resistance of the line when high frequency current is passed therethrough, besides the skin effect, there is the proximity effect. This occurs in such a manner that when a conductor is present in the proximity of an opposed conductor, high frequency current which concentrates near the surface of the conductor due to the skin effect produces a counter electromotive force in the opposed conductor, changing the current distribution.
The multiconductor cable brings about a difference in current phase between the conductors disposed at different distances from the center. And the nearer to the center is an electric wire disposed, the greater is the number of electric wires from which it receives the effect; therefore, as shown in FIG. 12, electric wires disposed nearer to the center have, as a result, a current y flowing therethrough which has a component opposite in direction to a current x which flows through outer electric wires, so that a circulating current flows through the line, resulting in an increase in resistance. Since passing a large, high frequency current is attended by a large loss due to this resistance, the multiconductor cable has not been suitable for use as a line for passing high frequency current. In FIG. 12, a multiconductor cable 31 is used as a high frequency current cable with the electric wires 32 bundled at each end and having a crimp terminal 33 attached thereto.
In addition, the proximity effect can hardly be removed by the use of a litz wire. Particularly, in the terminal preparation, a number of litz wires are simultaneously soldered for unification, whereby a difference in current phase tends to occur due to the difference in spatial arrangement when individual litz wires are stranded, thus resulting in an increase in resistance.
Accordingly, the invention has an object to solve the problems by providing a high frequency current multiconductor cable and a feeding equipment for one or more movable bodies using the high frequency current multiconductor cable, which cable suffers less loss due to resistance when high frequency current is passed and therefore is usable as an induction cable, besides being inexpensive and easy to prepare its terminals.
To achieve this object, the high frequency current multiconductor cable of the invention is a multiconductor cable comprising a plurality of covered electric wires, characterized in that a current balancing circuit is added for high frequency current flowing through each electric wire, and the current balancing circuit is formed by bundling electric wires equi-spaced from the center of the cable and by passing the bundles through a magnetic body in such a manner that ampere-turns or current densities become the same among the wires.
According to such arrangement, the counter electromotive force produced due to the difference in spatial arrangement when the electric wires of the feeder are stranded is cancelled by a current balancing circuit, forcing the individual electric wires of the feeder to take exactly the same current phase and current value, with the result that an increase in resistance due to the proximity effect is prevented; therefore, a line which suffers less resistance loss is obtained.
Further, a power feeding equipment for one or more movable bodies which uses the high frequency current multiconductor cable of the invention is a feeding equipment comprising an induction line extending along a moving path of the one or more moving bodies and supplying a constant high frequency current from a power source device, and a pickup coil provided in each moving body and being fed with power from the induction line in a contactless manner, characterized in that the foregoing induction line is formed by using the high frequency current multiconductor cable.
According to such arrangement, even when the induction line is arranged to extend for a long distance, an increase in resistance due to the proximity effect can be suppressed by means of the current balancing circuit, and the induction line can be formed by using the multiconductor cable. Furthermore, the use of the multiconductor cable eliminates the need for soldering, facilitates the terminal preparations, largely improves working efficiency in laying out the cable, and reducing the cost of forming the induction line to about half as compared with the case of using a litz wire to form the induction line, thereby realizing a cost reduction to a great extent.